A check valve can be located in an intake passage leading to a cylinder in an engine to obstruct back-flow of fluid out of the cylinder into the intake passage. In such an arrangement, a trapped volume is defined by the portion of the intake passage between the check valve and cylinder.
Increasing the pressure in the trapped volume prior to the intake of air into the cylinder (i.e., prior to an intake portion of the engine cycle) can improve engine performance since such increased pressure can reduce the work of the engine required to draw air into the cylinder. Also, increasing the pressure in the trapped volume prior to an intake portion can resist back-flow of exhaust gas from the cylinder into the trapped volume. The pressure in the trapped volume prior to an intake portion is typically at least equal to the pressure upstream of the check valve.
The pressure in the trapped volume can be increased by allowing communication between the trapped volume and cylinder during the exhausting of exhaust gas from the cylinder (i.e., during an exhaust portion of the engine cycle) resulting in exhaust gas flowing from the cylinder back into the intake passage and reentering the cylinder during the next intake portion. The pressure in the trapped volume can also be increased by allowing communication between the trapped volume and cylinder during, for example, the compression of air in the cylinder (i.e., during a compression portion of the engine cycle) resulting in some of the fluid in the cylinder flowing back into the intake passage and reentering the cylinder during the next intake portion. In both cases, the check valve obstructs fluid back-flow further into the intake passage and the pressure in the trapped volume increases.
The pressure in the trapped volume prior to an intake portion can be further affected by locating a port on the intake passage so that the port communicates with the trapped volume, and connecting a chamber having a fixed volume to the port to allow communication between the chamber and trapped volume. The effective volume of the trapped volume is thereby increased by an amount approximately equal to the volume of the chamber. The chamber may have an additional inlet to enable fluid, such as air, to flow into the chamber to further affect the pressure therein.
Such arrangements, however, can employ a chamber having a fixed volume. This can limit control of the pressure in the trapped volume prior to an intake portion. The optimum pressure in and the optimum volume of the trapped volume prior to an intake portion can vary depending on the operating condition of the engine.